Processing of waste incineration ashes

ABSTRACT

The invention relates to a method for processing waste incineration ashes, in particular domestic waste incineration ashes, in which a process for classifying the ashes and a process for recovering phosphates from the ashes are combined. In said method, the ashes are subjected to a wet classification process during which the ashes are mixed with a liquid, and the ashes are treated with an acidic aqueous solution to redissolve the phosphates, whereupon the phosphates contained in the solution are isolated. The liquid with which the ashes are mixed during the wet classification process is the acidic aqueous solution with which the ashes are treated to redissolve the phosphates.

The invention relates to a method for processing incinerator bottom ash,in particular municipal incinerator bottom ash (MIBA).

The ash which arises in the incineration of waste, in particular ofdomestic waste and industrial waste, cannot be easily disposed of orrecycled since the ash contains contaminants and thus requires a specialtreatment due to applicable relevant statutory provisions. The operatorsof incinerator plants therefore currently usually follow the procedurethat the arising ash is completely landfilled, which is, however,associated with relatively high costs, or it is utilized subject to highconstraints, e.g. as a low-classification building material

It is therefore the object of the invention to provide a possibility ofeconomically utilizing at least a portion of the incinerator bottom ash.

This object is satisfied by the features of claim 1 and in particular bya method for processing incinerator bottom ash, in particular municipalincinerator bottom ash (MIBA), in which a method for classifying the ashand a method for reclaiming phosphates from the ash are combined withone another. The ash is subjected to a wet classification and is in thisrespect mixed with a liquid. To resolve the phosphates, the ash istreated with an acidic watery solution, with the phosphates contained inthe solution subsequently being isolated. Provision is made Inaccordance with the invention that the liquid with which the ash ismixed within the framework of the wet classification is the acidic watersolution with which the ash is treated for resolving the phosphates.

It has been found that a wet classification of incinerator bottom ashopens up the possibility of separating the ash into a contaminatedportion and a low-contaminant or contaminant-free portion, with thelow-contaminant or contaminant-free portion being so large—with respectto the dry weight of the ash forming the starting product—that aneconomically sensible ash processing is already possible without theadditional phosphate reclamation by wet classification with subsequentutilization of the low-contaminant or contaminant-free portion, forexample in road construction.

The method combination in accordance with the invention is particularlyadvantageous because the phosphate reclamation makes use of thecircumstance that an interaction of the ash with a liquid anyway takesplace in the wet classification.

The inventors have recognized that the mixing of the ash with liquidtaking part in the wet classification can simultaneously form a methodstep in which the ash is treated with an acidic watery solution, whichmakes it possible to dissolve the phosphates contained in the ash. Ithas furthermore been recognized that the use of an acidic environment isuncritical both in a technical aspect and in an economic aspect withregard to the wet classification. An acid-resistant design of thedevices used for the wet classification is, for example, possiblewithout problem with an acceptable effort.

A simplified cost/benefit balance of the combined method in accordancewith the invention is therefore in principle characterized in that thecosts for the erection and operation of a plant suitable for the methodin accordance with the invention as well as the costs for the propertreatment, in particular landfilling, of the remaining contaminated ashportion, are to be set against the proceeds from the utilization of thelow-contaminant or contaminant-free ash portion and from the utilizationof the acquired phosphate. It must moreover be taken into account thatthe operators of incinerator plants are willing to pay for the removalof the ash arising in the incinerator in order not to have to take overthe complicated handling themselves. The obtaining of the ash to beprocessed is thus already associated with proceeds for an operator ofthe method in accordance with the invention.

It is thus the invention which in this manner for the first time makespossible a processing of incinerator bottom ash which both can becarried out technically and is also economically interesting.

Preferred embodiments of the invention are also set forth in thedependent claims, in the description and in the drawing.

A substantially closed liquid circuit from which at least a portion ofthe acidic watery solution is removed, in particular temporarily, forthe isolation of the phosphates is preferably used for the wetclassification of the ash. The removal in particular takes place in anongoing or suspended wet classification. Accordingly, either apractically permanent parallel operation or an alternating operation istherefore possible in that the wet classification is temporarilysuspended and the total solution is removed for the purpose of isolatingthe phosphates.

The removal of the solution for the isolation of the phosphates cangenerally take place in an ongoing process, with it alternatively alsobeing possible only to carry out the removal at specific times.

The isolation of the phosphates is in particular started in dependenceon the pH of the acidic watery solution.

The isolation of the phosphates preferably takes place in a device whichis separate from a device for treating the ash with the solution and towhich the solution can be supplied in accordance with a removal whichcan be controlled or regulated. In this respect, the removal inparticular takes place in dependence on the pH of the solution.

In accordance with an embodiment of the invention, water is provided forpreparing the acidic watery solution, with an acid being supplied to thewater. In this respect, in particular citric acid or sulfuric acid isused since it can be obtained comparatively inexpensively, withalternatively e.g. also sulfuric acid being able to be used.

The isolation of the phosphates in particular takes place byreprecipitation. The methods and devices to be used for this purpose aregenerally known per se so that they will not be looked at in any moredetail.

The reclamation of the phosphates is promoted by higher temperatures ofthe acidic watery solution without hereby impairing the wetclassification. When taking account of the energy input required for theheating of the acidic watery solution, it was found that an economicoperation is already possible at temperatures of the acidic waterysolution in the range from 20 to 40° C. Consequently, for a plant whichis suitable for carrying out the method in accordance with theinvention, a temperature of the acidic watery solution can be selectedsuch that the plant can be operated overall in an economic optimalrange.

In accordance with a preferred embodiment of the invention, the ash isclassified into at least one contaminated fine fraction and at least onelow-contaminant or contaminant-free coarse fraction in the wetclassification while using classification processes which are gentle onthe grain. Provision is in particular made that the ash is classifiedonly by wet classification and/or that the ash is completely classifiedinto at least one contaminated portion and at least one low-contaminantor contaminant-free portion.

This embodiment is based on the recognition that on a processing ofincinerator bottom ash the concentration of relevant contaminantscontained in the ash in a fine fraction, that is in one or more portionshaving a relatively low maximum grain size, can be economicallyinteresting if it is possible to keep the portion of this fine fractionin the starting material, that is in the ash introduced into theprocessing, as small as possible.

The inventors have recognized that this condition can be satisfied whenprovision is made that it is prevented as much as possible in theprocessing of the ash that the particles forming the ash are comminutedsince a comminution of the ash produces additional surfaces to whichcontaminants can bond, which has the consequence that the contaminatedportion increases, and indeed in a manner such that that portion of theash which cannot be profitably recycled, but must rather be expensivelylandfilled, is too large.

In this respect, this embodiment does not reach its goal in that theknown dry classification is modified, but rather in that the incineratorbottom ash is subjected to a generally known wet classification. Theinventors have recognized that the circumstance can be utilized thatparticularly a wet classification allows the use of classificationprocesses which are particularly gentle on the grain. The skilled personunderstands classification processes gentle on the grain as such methodsin which the particles to be classified are not comminuted or destroyedand in which in particular also no dust arises so that the grain sizedistribution of the incoming material is practically unchanged withrespect to that of the outgoing material overall, that is of allfractions together arising in the classification.

This idea of subjecting incinerator bottom ash to a wet classification,since particularly a wet classification allows a treatment of the ashwhich is particularly gentle on the grain, and furthermore ofconfiguring this wet classification such that an ash portion comprisingone or more fine fractions has a grain size distribution having an upperlimit such that this ash portion, on the one hand, contains all relevantcontaminants, where possible, and, on the other hand, is as small aspossible and makes it possible that only a relatively small portion ofthe ash cannot easily be recycled due to its contaminant charge, whereasa comparatively large low-contaminant or contaminant-free ash portioncan be supplied to recycling.

A possibility is hereby provided of processing incinerator bottom ash inwhich a significant portion of the ash can be supplied to aneconomically interesting recycling in accordance with even strictstatutory provisions.

The wet classification is preferably carried out such that the lowerlimit of the grain size in the fine fraction is 0 μm and the upper limitof the grain size approximately lies in the range from 50 to 500 μm, inparticular approximately lies in the range from 200 to 300 μm, and ispreferably approximately 250 μm.

The ash is preferably subjected to a mechanical pretreatment, inparticular a thy pretreatment, in which metals parts and non-incineratedimpurities are removed from the ash prior to the wet classification, inparticular prior to the introduction into a processing plant. The ashcan be moist in this respect. Such a pretreatment is, however, notcompulsory for the method in accordance with the invention. It hasnevertheless been found that the method in accordance with the inventioncan be carried out particularly advantageously when the ash introducedinto the processing plan has a specific grain size distribution.Provision is preferably made in this connection that the ash coming fromthe incinerator plant is pretreated such that the ash is introduced intothe wet classification, in particular into the processing plant with agrain size distribution whose upper limit does not amount to more than100 mm, with in particular the upper limit lying in the range from 40 to50 mm, and preferably amounting to approximately 45 mm. As mentioned atanother passage, it is in particular of advantage with respect to avisual screening of metals for the purpose of separating the metals andthus with respect to a preferred embodiment of the invention if theseparation does not take place in a dry manner, but rather the metalsare previously “washed along”.

Provision is made that the following steps are carried out after oneanother in time in the wet classification: The ash is first mixed withthe acidic watery solution. Subsequently, at least one coarse fractionis separated from the product produced in this process. A sieve deviceis in particular used in this respect. At least one second coarsefraction is then separated from the product liberated from the firstcoarse fraction, in particular using an upflow technique. The finefraction arising in this process subsequently has liquid removed fromit. In particular a chamber filter press is used in this respect.

Provision can be made in a possible embodiment of the invention that atleast one parameter of a liquid used for the wet classification is heldbeneath or above a predefined limit value. In this respect, liquid is inparticular expelled out of a liquid circuit as soon as the limit valueis reached, in particular exceeded or fallen below.

This embodiment can in particular be of practical significance when, onthe one hand, costs are to be saved and, on the other hand, it should beprevented that specific components are “dragged” onto the ash. Suchcomponents can in particular be salts, for example predominantlychlorides and sulfates. The concentration of these components can bedetermined, for example, by a conductivity measurement in the liquid,i.e. the monitored parameter in the liquid circuit can in particular bethe electrical conductivity. Accordingly, liquid is only expelled out ofthe circuit when the conductivity has reached the predefined limitvalue. The consumption of fresh liquid, in particular water, is herebyminimized, on the one hand, whereby costs are saved. On the other hand,it is prevented that the or each low-contaminant or contaminant-freecoarse fraction contains too high a portion of the respectivecomponents, in particular of salts. The limit value can in particular bemade dependent on the wishes of the respective plant operator or on thelocal wastewater treatment plant.

An advantage of the method in accordance with the invention comprises itbeing able, but not having to be, carried out independently of theincinerator plant delivering the ash in a technical method and plantrespect. In accordance with a preferred embodiment, provision istherefore made that the method in accordance with the invention iscarried out in a processing plant separate from an incinerator plant,with this, however, not being compulsory and with generally anintegration into an incinerator plant also being possible.

In accordance with a further embodiment of the invention, the processingof the ash in accordance with the invention can include a metalprocessing, i.e. the separation of metals, at one or more points. Thispreparation can include both an FE separation, that is a separation offerrous metals, and an NF separation, that is a separation ofnon-ferrous metals. FE separators or NF separators can consequently beused for this processing. Alternatively or additionally, a visualscreening can take place. This visual screening can take place bothmanually and by machine. Numerous variants are generally conceivablewhich each allow a single-variety metal processing.

The metal processing preferably takes place at one or at eachcontaminant-free or low-contaminant coarse fraction before its dumping.

The separation of the metals in particular does not take place in a drymanner before or after the wet classification of the MIBA, but ratherafter the passing through of at least one part of the wetclassification. In other words, the metals are also taken along in thewet process or washing process, i.e. the metals are washed along. Thishas the advantage that the metals become very clean, i.e. the metalsbecome so pure due to the washing that they can be recognized visuallywith reference to their respective colors, whereby a visual screening ofthe metals—manually or by machine—is improved or is made possible atall. The yield of metals is also increased by this “ washing along”. Thetaking along of the metals in the wet process or washing process, i.e.the “washing along” of the metals, can also take place when no visualscreening of any type takes place in the separation of the metals. Themetals which are “washed along” can also be separated in a mannerconventional per se using known metal separators.

In this manner, the economy of the ash processing can be substantiallyincreased.

The object is moreover satisfied by a processing plant for incineratorbottom ash, in particular for municipal incinerator bottom ash (MIBA),which is configured for classifying the ash and for reclaimingphosphates from the ash. The plant comprises a treatment device in whichthe ash can be treated with an acidic watery solution for resolving thephosphates and an isolating device in which the phosphates contained inthe solution can be isolated, with the plant being configured for a wetclassification of the ash and in this respect being configured for amixing of the ash with a liquid, and with the liquid with which the ashcan be mixed within the framework of the wet classification being theacid solution with which the ash can be treated for resolving thephosphates.

The plant is in particular configured for carrying out a method of thekind set forth here.

In a preferred embodiment of the plant, the isolation device is separatefrom the treatment device, with the solution being able to the suppliedfrom the treatment device to the isolation device by means of a removaldevice. The removal device can preferably be controlled or regulated,and indeed in dependence on the pH of the solution.

The plant preferably has at least one substantially closed liquidcircuit at least for the wet classification. It can hereby be achievedthat the ash interacts for a relatively long period and comparativelyintensely with the liquid, that is the acidic watery solution.

The plant preferably comprises wet classification devices which aregentle on the grain, with the plant being configured such that the ashcan be classified into at least one contaminated fine fraction and intoa least one low-contaminant or contaminant-free coarse fraction. Onlywet classification devices gentle on the grain are preferably providedin the plant.

In accordance with a further preferred embodiment, the processing plantin accordance with the invention is configured such that the lower limitof the grain size in the fine fraction arising in the wet classificationis 0 μm and the upper limit of the grain size approximately lies in therange from 50 to 500 μm, in particular approximately lies in the rangefrom 200 to 300 μm, and is preferably approximately 250 μm.

Provision is in particular made that the plant in accordance with theinvention comprises a mixing stage in which the plant is mixed with theliquid, with in particular the mixing stage comprising or forming thetreatment device, or vice versa.

A common device in which the ash is both mixed with a liquid within theframework of the wet classification and is treated with an acidic waterysolution within the framework of the phosphate reclamation can beadvantageous, but is not compulsory. It is alternatively also possibleto provide a respective mixing stage and a treatment stage separatelyand behind one another in the process direction so that, for example,first the ash is only mixed with water and subsequently an acid issupplied to the mixture in a separate device.

It is generally also possible in accordance with the invention toreclaim other materials from the incinerator bottom ash alternatively oradditionally to phosphates in that the wet classification is utilizedand thus the circumstance that a resolution of materials contained inthe ash takes place due to the intense contact of the ash with a liquid,which anyway takes place, wherein as required the liquid used in the wetclassification is enriched in a suitable manner. This recycling ofusable materials from incinerator bottom ash treated with a suitableliquid also represents an independent separately claimable aspect of theinvention in conjunction with a wet classification of the ash.

Whereas previously in practice the MIBA was stored for a relatively longtime period of e.g. three months before a processing or treatment wasstarted, provision is preferably made in accordance with the inventionthat the processing or treatment of the ash is started comparativelysoon after its production. This has the advantage that a bonding orsintering of the ash which has been recognized as disadvantageous doesnot take place or only takes place to a non-critical degree. Stored ash,in contrast, is prone to bonding or sintering, and indeed due to thechemical reactions taking place during the storage. Bonded ash mustfirst be separated before or during the processing or treatment by“heavy equipment”, i.e. with a mechanical effort which is not exactlygentle. A storage of the ash also has the consequence that containedmetals can be highly charged with ash, which makes a visual screening ofthe metals more difficult or impossible.

A disadvantageous bonding or sintering of the ash cannot occur at all orthe disadvantageous chemical reactions are shortened by an earlyprocessing or treatment of the MIBA in a wet process. After thisprocessing or treatment, a disadvantageous bonding or sintering of theash can therefore no longer occur.

The invention will be described in the following by way of example withreference to the drawing whose only FIGURE schematically shows anembodiment of an apparatus in accordance with the invention in which amethod in accordance with the invention can be carried out.

The apparatus in accordance with the invention comprises a processingplant 11 having various equipment which will be described in more detailin the following. The processing plant 11 is independent of anincinerator plant. The processing plant 11 can in particular be erectedat any desired location and can be operated separately from anincinerator plant, with this, however, not being compulsory andgenerally an integration into an incinerator plant also being possible.

It is possible with the plant 11 in accordance with the invention toprocess the incinerator ash such as arises in the incinerator in themanner explained in the following. A pretreatment of any kind or apreparatory processing of the ash A is in particular not absolutelynecessary. Nevertheless, a preferred embodiment of the inventionprovides that the incinerator bottom ash is subjected to a mechanicalpretreatment, in particular a dry pretreatment, prior to theintroduction into the processing plant 11 in which pretreatment metalparts and non-incinerated impurities are removed from the ash.

The processing method in accordance with the invention and theprocessing plant 11 in accordance with the invention are in particularsuitable for the processing of municipal incinerator bottom ash. Theinvention is, however, not limited to this. It is thus also generallypossible to process other incineration residues in the manner inaccordance with the invention, for example ash or slag, which arises onthe incineration of industrial waste.

In the embodiment of the invention explained here, the ash A introducedinto a mixing stage 21 of the plant 11 and previously liberated frommetal parts and non-incinerated impurities is separated into threefractions I, II and III, namely into a fine fraction I and into twocoarse fractions H and III. The coarse fractions II and II are notcontaminated and can be stored on waste dumps 29, 31 until they aresupplied to a use. The contaminants originally contained in the ash Aare located in the fine fraction I which cannot be easily utilized andwhich is stored on a landfill 33, for example.

The contaminants usually contained in municipal incinerator bottom ash(in the following abbreviated to MIBA) are generally known. Sulfate,chloride, anhydride and TOC (total organic carbon) can be named asexamples here. It must be mentioned with respect to the anhydride thatit is also counted among the contaminants here with respect to apossible recycling of MIBA, for example in road construction, since itsvolume is substantially enlarged, i.e. swells, due to the absorption ofwater and can consequently develop a bursting effect, which can resultin a destruction of the respective constructions.

The processing of the ash A takes place by wet classification in theplant 11 in accordance with the invention.

For this purpose, the ash A is mixed with a liquid in the mixing stage21. Water W is preferably used as the liquid. With respect to aparticularly advantageous embodiment of the processing in accordancewith the invention, which will be looked at in more detail in thefollowing, a specific watery solution, namely an acidic watery solution,is used as the liquid.

For reasons of simplicity, the liquid used here will also simply becalled “water” or “solution” in the following.

The mixing of the ash A with the water can take place in the sense of asteeping or mashing. Accordingly, the mixing stage 21 can also be calleda steeper or masher.

The mixing of the ash A in the mixing stage 21 takes place in a mannergentle on the grain to at least largely avoid a comminution of theintroduced ash particles. Where provision is made at all, a mechanicalinfluence on the ash A in the mixing stage can take place by means of avibration plate, for example.

A treatment of the ash A gentle on the grain does not only take place inthe mixing stage 21. The total plant 11 is rather configured for ashprocessing gentle on the grain. As already initially mentioned, theperson skilled in the art is familiar with the phrase “gentle on thegrain”. It is in particular understood by this that such devices ormethod steps in which the ash particles are comminuted are neitherdeliberately used nor accepted. A treatment gentle on the grainnaturally does not preclude ash particles from being separated from oneanother which originally only stick to one another.

It must be mentioned in this connection that the skilled person isadmittedly generally familiar with different wet classification methodswhich can be called gentle on the grain, but that the skilled personfurthermore also knows such methods which can be used within theframework of a wet classification and which should deliberately induceor accept a comminution of the particles to be classified. So-called logwashing can be named by way of example in this respect. The use of suchmethods of wet classification not gentle on the grain deliberately doesnot take place in accordance with the invention.

The water supplied to the mixing stage 21 is provided by a closed watercircuit W. The designation as “closed” naturally does not preclude thatconsumed liquid can be replaced and—provided provision is made in theembodiment described here—liquid can also be removed for an additionalreclamation of phosphates P explained in the following without a returninto the circuit W.

To establish the mentioned acidic environment, the mixing stage 21moreover has an acid S supplied to it which is in particularcomparatively inexpensively available citric acid or sulfuric acid. Thementioned liquid circuit W is therefore in the preferred embodiment ofthe invention explained here a circuit of an acidic watery solution. Anacidic environment is neither absolutely necessary nor disadvantageousfor the wet clarification in accordance with the invention per se sinceall the relevant plant parts can be configured as acid-resistant withoutproblem.

The ash A which is mixed with the water, i.e. the steeped or mashed ash,which still contains all three initially mentioned fractions I, II andIII, is subsequently supplied to a first classification stage 17 whichis a sieve device which is configured such that all ash particles havinga grain size of more than 4 mm are separated.

In this first classification stage 17, the ash is sluiced with water Wcoming from the mentioned circuit and is sieved at the named 4 mm.

As regards the grain sizes of the ash particles mentioned in connectionwith the explanation of this embodiment, provision is made there thatwith a mechanical pretreatment, in particular a dry pretreatment of theash coming from the incinerator plant metal parts and non-incineratedimpurities are removed, wherein this pretreatment takes place such thatthe grain size distribution of the ash A introduced into the mixingstage 21 has an upper limit of approximately 45 mm.

The first coarse fraction III separated by means of the firstclassification stage 17 thus has a grain size distribution ofapproximately 4 to 45 mm. This coarse fraction III is conducted out ofthe plant 11 and is stored on the already mentioned dump 29.

The remaining ash portion having a grain size distribution ofapproximately 0 to 4 mm, which thus includes the initially mentionedfine fraction I and the further coarse fraction II, is subsequentlysupplied to a second classification stage which comprises an upflowclassifier 15 having an upstream hydrocyclone 13. Such arrangements aregenerally known so that the design and operation of this secondclassification stage will not be looked at in any more detail. It mustbe emphasized that the particles to be classified are treated extremelygently both in a hydrocyclone and in an upflow classifier. This meansthat the grain size distribution of the ash portion coming from thefirst classification stage 17 is also practically not changed by thesecond classification stage 13, 15.

In the embodiment explained here, the second classification stage 13, 15is configured or set such that a second coarse fraction II is separatedfrom the introduced product and has a grain size distributionapproximately in the range from 0.25 mm to 4 mm. This coarse fraction IIis supplied to a sieve device 35 which can, for example, be a so-called“E sieve” which comprises two sieve decks, wherein the material on theupper sieve deck is sluiced with water W and is dewatered on the lowersieve deck. The water W is in this respect removed from the mentionedcircuit and is also supplied to this circuit again.

The further coarse fraction II dewatered in this manner is alsosubsequently conducted out of the plant 11 and stored on the alreadymentioned dump 31.

As mentioned above, the second classification stage 13, 15 is set suchthat the remaining fine fraction I after the separation of the secondcoarse fraction II has an upper limit of the grain size of approximately0.25 mm, that is of approximately 250 μm. The configuration of the plant11 and in particular of the second classification state 13, 15 such thatthis upper limit for the grain size of the fine fraction I is exactlyobserved is not compulsory. The upper limit for the grain size of thefine fraction I is in particular selected in dependence on theintroduced ash A and in particular on the manner and amount of thecontaminants contained therein and to be concentrated in the finefraction I such that it is ensured that all relevantparticles—optionally with the exception of a residue which can betolerated with respect to applicable statutory provisions—bind to theparticles forming the fine fraction I. This upper limit is in particularselected such that it is neither too low, since otherwise the nexthigher coarse fraction is also contaminated to a no longer tolerabledegree, nor too low, since otherwise the dry weight portion of the finefraction I in the introduced ash A is unnecessarily large.

It is achieved in this manner that all relevant contaminants of the ashA introduced into the plant 11 are located in the fine fraction I whichis moreover minimized with respect to its dry weight portion in theintroduced ash A. The dumped coarse fractions III and II are liberatedfrom at least a large portion of the contaminants in this respect andcan be supplied to a recycling, for example in road construction, inagreement with the respectively applicable statutory regulations.

Liquid is subsequently removed from the fine fraction I coming from thesecond classification stage 13, 15 in a round thickener 23.

Subsequently, the fine fraction I is supplied to a chamber filter press19 by means of an eccentric pump 25. Instead of a chamber filter press,a cyclone can also be provided, for example, to further dewater the finefraction I. The use of a chamber filter press has, however, been foundto be particularly advantageous to date.

The fine fraction I conducted from this dehumidification stage formed bythe round thickener 23, the eccentric pump 25 and the chamber press 19is dehumidified so much that it is semisolid and can thus be landfilled.The water W arising in this dehumidification stage is again supplied tothe circuit.

Trials have shown that the manner of wet classification of MIBAdescribed here having an upper limit of the original grain sizedistribution of approximately 45 mm produces a fine fraction I havinggrain sizes of up to 0.25 mm, wherein the fine fraction I, on the onehand, contains all the relevant contaminants and, on the other hand,only represents approximately 10% of the dry weight of the ash Aintroduced into the plant II. This means that a dry weight portion ofapproximately 90% of the ash A introduced into the plant 11 can beutilized without problem with the two produced coarse fractions III andII since these coarse fractions III and II are low in contaminants orfree of contaminants.

The practical realization of the invention is already economicallyinteresting to a high degree due to this utilization possibility forincinerator bottom ash which had previously not been consideredrealisable despite the costs for the construction and the operation ofthe processing plant 11 in accordance with the invention. In addition,there is the fact that the operators of incinerator plants have aninterest in not themselves having to provide a disposal of theincinerator bottom ash according to regulations since to date thisdisposal has taken place by landfilling or by utilization subject tohigh constraints of the total ash arising in the incinerator, which isassociated with high costs due to the contaminants contained and due tothe statutory provisions in this respect. The operators of incineratorplants are consequently willing to pay for the removal of theincinerator bottom ash. The economy of the ash processing in accordancewith the invention is thereby further increased since the acceptance ofthe ash to be introduced into the processing plant can already beassociated with income. Provided that the mentioned pretreatment of theash coming from the incinerator plant is carried out at all for removingmetal parts and/or non-incinerated impurities, this pretreatment doesnot stand in the way of the economy of the procedure in accordance withthe invention.

In the embodiment of the invention described here, the economy of theash processing is furthermore further increased in that materials arerecycled from the ash A introduced into the plant 11 which can in turnbe supplied for utilization. This utilization of the ash (A), inparticular the reclaiming of phosphates explained in the following,represents an independent, separately claimable aspect of the inventionindependently of the wet classification of the ash A.

As mentioned, this further utilization of the incinerator bottom ash inthe embodiment described here relates to the reclamation of phosphatesP. In this respect, the circumstance is exploited that the ash A anywayinteracts with a liquid in the above-described wet classification. Inparticular the closed liquid circuit W has the consequence that theliquid can interact a relatively long time and intensely with the ash A,which is utilized in accordance with the invention.

A resolution of phosphates P contained in the introduced ash A can thustake place by a suitable choice of the liquid, wherein these phosphatesP can be isolated again in a further method step.

As already mentioned above, in the preferred embodiment, water W is usedas the liquid for the wet classification which is enriched in the mixingstage 21 with acid S, in particular with citric acid or sulfuric acid.The mixing or steeping or mashing of the ash A with the liquid whichtakes place in the wet classification thus simultaneously represents atreatment of the ash A with an acidic watery solution which has theconsequence of a resolution of the phosphates P contained in the ash A.

Within the framework of the wet classification of the ash A describedhere, for which an acidic environment is not compulsory, but is also notdisadvantageous since all relevant plant parts are configured asacid-resistant, this kind of reclamation of phosphates P is particularlyadvantageous since the mixing of the ashes A with the water or with theacidic watery solution and in particular the closed liquid circuitallows an intimate reaction of the ash A with the acidic water solutionwhich lasts a particularly long time. This combination—expressed inkeywords, that is the wet classification of incinerator bottom ash withan integrated reclamation of utilizable materials, in particularphosphates—generally likewise represents an independent, autonomous andseparately claimable aspect of the invention.

The resolution of the phosphates P is promoted by a higher temperatureof the acidic watery solution without hereby impairing the wetclassification. While taking account of the energy input required forthe heating of the liquid and the associated costs, the temperature isselected such that the plant can be operated in an economic optimalrange overall. It has been found that this is already possible at atemperature of the acidic watery solution in the closed circuit in therange from 20 to 40° C.

The removal of liquid, including the phosphates P resolved therein, alsocalled a solution L in the following, can take place without problemduring the ongoing wet classification operation.

An ongoing removal of the solution L is generally possible. Provisioncan alternatively be made that a specific quantity of the solution L isonly removed from the circuit W at specific points in time. These pointsin time can in particular be selected in dependence on the pH of thecirculating liquid.

The removal of the solution L containing the resolved phosphates P cangenerally take place at any desired point of the liquid circuit W. Aremoval device can be provided for this purpose which can be controlledor regulated in dependence on the pH of the solution L.

The solution L is supplied to an isolating device 27 in which areprecipitation of the phosphates P takes place in a generally knownmanner. The liquid remaining after the isolation of the phosphates P isagain supplied to the circuit W.

In this manner, a valuable resource which can in turn be supplied to aprofitable utilization is produced with the phosphates P which areisolated from the solution L taken from the circuit W.

Since the reprecipitation of phosphates from a solution, includingmethods and devices to be used in this process, is generally known perse, it will not be looked it in more detail at this point.

It is generally also possible in accordance with the invention torecycle other materials from the incinerator bottom ash alternatively oradditionally to phosphates in that the wet classification is utilizedand thus the circumstance that a resolution of materials contained inthe ash takes place due to the intense contact of the ash with a liquid,which anyway takes place, wherein as required the liquid used in the wetclassification is enriched in a suitable manner. This recycling ofusable materials from incinerator bottom ash treated with a suitableliquid also represents an independent separately claimable aspect of theinvention independently of a wet classification of the ash.

In the embodiment shown in the FIGURE, a measuring device in the form ofa potentiometric probe 41 is connected before the round thickener 23 andthe electrical conductivity of the liquid can be measured with it. Ifthe conductivity reaches a predefined value, which can be predefined,for example, by the local operator of the processing plant or of thewastewater treatment plant, a predefined quantity of liquid can beexpelled and can be replaced with fresh liquid, in particular with freshwater. The water expulsion E can—as shown by way of example in theFIGURE—take place after the round thickener 23 viewed in the processdirection.

Provision is furthermore made in the embodiment shown here that arespective metal processing 37, 39 takes place before the dumping of thetwo coarse fractions II, III. This can take place in a varied manner independence on the circumstances and on the demands, as has already beenmentioned by way of example in the introduction. The metal processingpreferably takes place such that the metals are taken along, i.e.“washed along” in the wet process or washing process before theirseparation so that a visual screening is improved or made possible atall since the metals become particularly clean by this taking along ofthe metals in the wet process.

REFERENCE NUMERAL LIST

11 processing plant

13 hydrocyclone

15 upflow classifier

17 sieve device

19 chamber filter press

21 mixing stage

23 round thickener

25 eccentric pump

27 isolating device

29 dump

31 dump

33 landfill

35 sieve device

37 metal processing

39 metal processing

41 measuring device

A ash

I fine fraction

II coarse fraction

III coarse fraction

W water, water circuit

L watery solution

S acid

P phosphates

E water expulsion

1. A method for processing incinerator bottom ash (A) in which a methodfor classifying the ash (A) and a method for reclaiming phosphates (P)from the ash (A) are combined with one another, wherein the ash (A) issubjected to a wet classification and is in this respect mixed with aliquid (L); wherein the ash (A) is treated with an acidic waterysolution (L) for resolving the phosphates (P) and subsequently thephosphates (P) contained in the solution (L) are isolated; and whereinthe liquid with which the ash (A) is mixed within the framework of thewet classification is the acidic watery solution (L) with which the ash(A) is treated for resolving the phosphates (P).
 2. The method inaccordance with claim 1, wherein a substantially closed liquid circuitis used for the wet classification of the ash (A), from which liquidcircuit at least one portion of the acidic watery solution (L) isremoved for the isolation of the phosphates.
 3. The method in accordancewith claim 1, wherein the ash (A) is classified into at least onecontaminated fine fraction (I) and into at least one low-contaminant orcontaminant-free coarse fraction (II, III) in the wet classificationwhile using classification processes gentle on the grain.
 4. The methodin accordance with claim 1, wherein the ash (A) is only classified bywet classification; and/or wherein the ash (A) is completely classifiedinto at least one contaminated portion (I) and into at least onelow-contaminant or contaminant-free portion (II, III).
 5. The method inaccordance with claim 1, wherein the ash (A) is subjected to amechanical pretreatment, in which metal parts and non-incineratedimpurities are removed from the ash (A) prior to the wet classification;and/or wherein the ash coming from the incinerator plant is pretreatedsuch that the ash (A) is introduced into the wet classification with agrain size distribution whose upper limit does not amount to more thanapproximately 100 mm.
 6. The method in accordance with claim 1, themethod comprising the following steps which are carried out after oneanother in time during the wet classification: the ash (A) is mixed withthe acidic water solution (L); at least one first coarse fraction (III)is separated from the product produced in this process; at least onesecond coarse fraction (II) is separated from the product liberated ofthe first coarse fraction (III); and liquid (L) is removed from the finefraction (I) produced in this process.
 7. The method in accordance withclaim 1, wherein water (W) is provided for preparing the acidic waterysolution (L) and an acid (S) is supplied to the water (W).
 8. The methodin accordance with claim 1, wherein the isolation of the phosphates (P)is started in dependence on the pH of the acidic watery solution (L). 9.The method in accordance with claim 1, wherein the phosphates (P) areisolated by reprecipitation.
 10. The method in accordance with claim 1,wherein the acidic watery solution (L) has a temperature in the rangefrom 20 to 40° C.
 11. The method in accordance with claim 1, wherein theisolation of the phosphates (P) takes place in a device (27) which isseparate from a device (21) for treating the ash (A) with the solution(L) and to which the solution (L) can be supplied in accordance with aremoval which can be controlled or regulated.
 12. The method inaccordance with claim 1, wherein the method is carried out in aprocessing plant (11) separate from the actual incinerator.
 13. Themethod in accordance with claim 1, wherein at least one parameter of aliquid used for the wet classification is held beneath or above apredefined limit value.
 14. A processing plant for incinerator bottomash (A) which is configured for classifying the ash (A) and forreclaiming phosphates (P) from the ash (A), wherein the plant (11)comprises a treatment device (21) in which the ash (A) can be treatedwith an acidic watery solution (L) for resolving the phosphates (P) andan isolating device (27) in which the phosphates (P) contained in thesolution (L) can be isolated; wherein the plant (11) is configured for awet classification of the ash (A) and in this respect is configured fora mixing of the ash (A) with a liquid (L); and wherein the liquid withwhich the ash (A) can be mixed within the framework of the wetclassification is the acidic watery solution (L) with which the ash (A)can be treated for resolving the phosphates (P).
 15. The processingplant in accordance with claim 14, in which the isolating device (27) isseparate from the treatment device (21), with the solution (L) beingable to be supplied to the isolation device (27) from the treatmentdevice (21) by means of a removal device.
 16. The processing plant inaccordance with claim 14, further comprising at least one substantiallyclosed liquid circuit for at least the wet classification.
 17. Theprocessing plant in accordance with claim 14, further comprising wetclassification devices which are gentle on the grain and the plant beingconfigured such that the ash (A) can be classified into at least onecontaminated fine fraction (I) and at least one low-contaminant orcontaminant-free coarse fraction (II, III).
 18. The processing plant(11) in accordance with claim 14, the plant (11) being configured suchthat the lower limit of the grain size in the fine fraction (I) is 0 μmand the upper limit of the grain size approximately lies in the rangefrom 50 to 500 μm.
 19. The processing plant (11) in accordance withclaim 14, further comprising a mixing stage (21) in which the ash (A) ismixed with the liquid (L), or vice versa.
 20. The apparatus inaccordance with claim 14, the apparatus being configured to carry out amethod for processing incinerator bottom ash (A).